package queue;

public class LoopQueue<E> implements Queue<E> {
    private E[] data;
    private int front,tail;
    private int size;

    public LoopQueue(int capacity){
        data = (E[]) new Object[capacity + 1];
        front = 0;
        tail = 0;
        size = 0;
    }

    public LoopQueue(){
        this(10);
    }

    public int getCapacity(){
        return data.length - 1 ;
    }

    public int getSize() {
        return size;
    }

    public boolean isEmpty() {
        return front == tail;
    }

    public void enqueue(E e) {
        if((tail + 1) % data.length == front){
            resize(getCapacity() * 2);
        }
        data[tail] = e;
        tail = (tail + 1) % data.length;
        size ++;
    }


    public E dequeue() {
        if(isEmpty()){
            throw new IllegalArgumentException("Cannot dequeue from an empty queue");
        }
        E ret = data[front];
        data[front] = null;
        front = (front + 1) % data.length;
        size -- ;
        if(size == getCapacity() / 4  && getCapacity() / 2 != 0){
            resize(getCapacity() / 2);
        }
        return ret;
    }

    public E getFront() {
        if(isEmpty()){
            throw new IllegalArgumentException("Cannot dequeue from an empty queue");
        }
        return data[front];
    }

    private void resize(int newCapacity){
        E[] newData = (E[]) new Object[newCapacity + 1];
        for(int i = 0;i < size ;i++){
            //将原先的front放置到0的位置
            newData[i] = data[(i+front) % data.length];
        }
        data = newData;
        front = 0;
        tail = size;
    }

    @Override
    public String toString() {
        StringBuffer res = new StringBuffer();
        res.append(String.format("Queue:size= %d,capacity=%d\n",size,getCapacity()));
        res.append("front[");
        for(int i=front;i != tail;i = (i+1) % data.length){
            res.append(data[i]);
            if((i + 1) % data.length != tail){
                res.append(",");
            }
        }
        res.append("]tail");
        return res.toString();
    }

    public static void main(String[] args) {
        LoopQueue<Integer> arrayQueue  = new LoopQueue<Integer>();
        for(int i = 0 ;i < 10 ;i++){
            arrayQueue.enqueue(i);
            System.out.println(arrayQueue);

            if(i % 3 == 2){
                arrayQueue.dequeue();
                System.out.println(arrayQueue);
            }
        }
    }
}


